The present invention relates to radio telecommunication systems. More particularly, and not by way of limitation, the present invention is directed to a system and method for dynamically controlling throughput over the air interface between a mobile terminal and a radio telecommunication network.
The length of the packet queue (PQ) in a Node-B (base station) is handled by High-Speed Downlink Packet Access (HSDPA) flow control (FC). The flow control process contends with two somewhat contradictory goals: (1) keep the PQ length short for low delay (low latency), which is good for time-sensitive traffic; and (2) keep the PQ length long enough to avoid under-utilization of the available radio bearer, as when there is an empty PQ buffer while there are packets waiting in the Radio Network Controller (RNC).
The existing HSDPA FC algorithm tries to fulfill both requirements by dynamically setting the shaping rate of the packet flow in the RNC. The shaping rate is set relative to a target delay according to the following algorithm:                If the estimated delay (PQ length) is smaller than the target delay, then HSDPA FC increases the shaper bit rate; and        If the estimated PQ length is larger than the target delay, then the HSDPA FC decreases the shaper bit rate.        
Performance of the Uu interface between the mobile terminal and the Node B depends highly on the target delay selected by the HSDPA FC algorithm.
The main problem with the existing HSDPA FC algorithm is that there is no target delay that is optimal for all types of traffic. Delay-sensitive traffic (for example, online gaming traffic) requires a very small target delay, while “throughput oriented” traffic (for example, downloading a large file) should use a higher target delay to avoid underutilization of the available radio resource. The existing HSDPA FC algorithm adjusts the shaper bit rate to match the target delay set by the operator, but it does not change the target delay. When a user utilizes services from both types, preference is usually given to the delay-sensitive traffic. It is acceptable if the download speed drops, for example 20 percent, but delay of online gaming traffic is far less tolerable.